"UNIT 6 The Lymphatic System (Chapter 20)"
UNIT 6 The Lymphatic System (Chapter 20) • Lymphatic System Overview • Lymphatic Vessels and Flow of Lymph • Lymphoid Cells, Tissues, and Organs (7th edition) Overview of the Lymphatic System • Major Components of the Lymphatic System (fig. 20.1) LYMPH - an extracellular fluid (ECF) similar to plasma; ECF is found in several places in the body: body tissues (ECF = interstitial fluid), blood (ECF = plasma), and lymphatic vessels (ECF = lymph) LYMPHATIC VESSELS - a network of vessels that carry lymph throughout the body, and eventually to the venous blood system LYMPHATIC TISSUE - protective tissue scattered throughout the body; lymphatic tissue is a specialized connective tissue containing large numbers of lymphocytes LYMPHATIC ORGANS - e.g. the spleen and thymus LYMPHOCYTES - white blood cells involved with immunity • The Lymphatic System and Cardiovascular System are collectively called the Circulatory System; the lymphatic system circulates lymph and the cardiovascular system circulates blood (7th edition) Overview of the Lymphatic System Major Functions of the Lymphatic System: • fluid balance - excess interstitial fluid from tissue spaces (interstitial spaces) is returned to the blood by the lymphatic capillaries; once interstitial fluid enters a lymphatic capillary it is called “lymph” every day, about 30 liters of fluid leave your blood capillaries and enter the interstitial fluid of the body tissues approximately 27 of those liters are reabsorbed back into the blood capillaries the remaining 3 liters move into the lymphatic capillaries, so that they are removed from the tissue • distribution - of hormones, nutrients, and waste products from the site of origin to general circulation the lymphatic system absorbs fats from the small intestines, and lymphatic vessels carry the fats to the bloodstream transport of lipid-soluble vitamins (A, D, E, and K) from the gastrointestinal tract to the blood • defense - microorganisms and antigens are destroyed by WBCs (7th edition) Lymphatic Vessels and Lymph Flow • LYMPHATIC CAPILLARIES (fig. 20.1) - are found in most tissues of the body; they differ from blood capillaries in several ways: they originate as blind pockets; each of the lymphatic capillaries has one closed end; extracellular fluid enters the lymphatic capillary through a flap-like minivalve they are larger in diameter than blood capillaries they have thinner walls than blood capillaries there are gaps between the endothelial cells that comprise the wall of the lymphatic capillary making them more porous; fluids can enter the lymphatic capillary but cannot leave • Lymphatic vessels - resemble veins in structure; from the capillaries, lymph moves into lymphatic vessels; they contain valves which keep the lymph moving in one direction through these low pressure vessels (7th edition) Lymphatic Vessels and Lymph Flow • In general a tissue will contain many more lymphatic vessels than veins but they will be much smaller • Lymph moves in response to: contraction of surrounding skeletal muscles (remember that veins return blood to the heart using a similar mechanism); like veins, lymph vessels have valves to keep the fluid moving in one direction contraction of smooth muscle in wall of the lymphatic vessel pressure changes in the thoracic cavity during respiration • Major lymph-collecting vessels: (fig. 20.2) THORACIC DUCT - largest lymph vessel; drains into the left subclavian vein; drains the entire body except the upper right quarter CYSTERNA CHYLI - expanded abdominal portion of the thoracic duct; this is where fat-filled vessels from the digestive tract enter the lymphatic system RIGHT LYMPHATIC DUCT - drains lymph from the upper right quarter of the body; drains into the right subclavian vein (7th edition) Lymphoid Cells, Tissues, and Organs • Types of Lymphocytes: T CELLS (T lymphocytes) - attack foreign cells or body cells infected by viruses; T cells mature and divide in the thymus; T cells are responsible for cell-mediated immunity (meaning that the protection is directly from living cells) B CELLS (B lymphocytes) - responsible for antibody-mediated immunity (=humoral immunity); a percentage of circulating B lymphocytes mature into PLASMA CELLS; plasma cells produce and secrete antibodies which destroy antigens NK CELLS (natural killer cells) - attack foreign cells and cells infected with viruses and cancer cells • LYMPHOID NODULES - lymphocytes densely packed into an area of areolar tissue occur in the connective tissue deep to the epithelia that line the respiratory, digestive, and urinary tracts have a central zone called a germinal center which contains dividing lymphocytes the boundaries of the nodule are not distinct because they have no fibrous capsule surrounding them (7th edition) Lymphoid Cells, Tissues, and Organs • LYMPH NODES (fig. 20.4) small oval lymphoid organs distributed along the lymphatic vessels; each lymph node is covered by a capsule of dense fibrous connective tissue; connective tissue strands call trabeculae extend inward to divide the node into compartments they filter the lymph, removing bacteria and antigens lymphocytes congregate, function, and proliferate in the lymph nodes lymph nodes are found throughout the body: superficial aggregations of lymph nodes are found in the inguinal, axillary, and cervical regions afferent lymphatic vessel - lymph vessel that carries lymph to the lymph node; as lymph flows through the lymph node it is exposed to B and T cells and macrophages; at least 99% of the pathogens in the lymph are removed efferent lymphatic vessel - lymph vessel that carries lymph away from the lymph node (7th edition) Lymphoid Cells, Tissues, and Organs SPLEEN • located in the superior, posterior, left abdominal cavity (fig. 20.5) • contains the largest collection of lymphoid tissue in the body • performs the same function for blood that lymph nodes perform for lymph; the spleen filters the blood and is involved with: removal of abnormal blood cells and other blood components by phagocytosis storage of iron from recycled RBCs initiation of immune responses by B cells and T cells in response to antigens in circulating blood • the spleen also acts as a blood reservoir • RED PULP vs. WHITE PULP: red pulp - area of the spleen that contains large numbers of RBCs; the structural framework of the red pulp consists of a network of reticular fibers; it is rich in macrophages; red pulp is mainly concerned with disposing of worn-out red blood cells and bloodbourne pathogens white pulp - area of the spleen that resembles lymphoid nodules; it is composed mostly of lymphocytes suspended on reticular fibers, and is involved with the immune functions of the spleen (7th edition) Lymphoid Cells, Tissues, and Organs • TONSILS Large lymphoid nodules in the walls of the pharynx and oral cavity (fig. 20.5) pharyngeal tonsil - also called the “adenoids” is located in the posterior superior wall of the nasopharynx palatine tonsils - a pair of tonsils located at the posterior margin of the oral cavity along the border along its boundary with the oropharynx lingual tonsil - located under the attached base of the tongue • PEYER’S PATCHES Peyer's patches are clusters of lymphoid nodules deep to the epithelial lining of the small intestine (fig. 20.5) contain lymphocytes and macrophages which remove microorganisms, debris, and antigens from the digestive tract • APPENDIX - large concentrations of lymphoid tissue are located in the wall of the appendix; thus, the appendix has some lymphatic function (fig. 20.5) (7th edition) NOTE: For a good review of some of what we have just covered in the lymphatic system, view the Interactive Physiology tutorial “The Immune System: Anatomy Review”; it is located in Chapter 21 of the textbook website (7th edition) This concludes the current lecture topic • Be sure to read the next lecture topic: Immunity (Chapter 21) (close the current window to exit the PowerPoint and return to the Unit 6 Startpage) (7th edition)